Crystal chemistry of tetraradial species. Part 2. Crystal structures of Et₄NI, Ph₄PBr•H₂O, and Ph₄PBr•2H₂O

Abstract

The crystal structure of Et4NI (14,a = 8,860(2) A, c = 6.932() A, Z = 2) has been redetermined and those of Ph4PBr.H20 ( p i , n = 10.005(3) A, b = 10.659(2) A, c = 10.697(4) A, % = 102.61(2)", P = 83.39(3)", y = 108.09(3)", Z = 2) and Ph4PBr.2H20 (Pnma, a = 16.255(4) A, b = 10.810(4) A, c = 12.667(9) A, Z = 4) have been determined for the first time. In the Et4NI structure Et4Nt cations in an extended S4 conformation and I-anions are arranged in a zincblende-type packing. The two hydrate structures are ionic and very similar. The anion in the monohydrate is a centrosymmetric cyclic dimer [Br2(0~2)2]2-; in the dihydrate the anion, which is an almost planar infinite 412]z chain Ilb, appears to be of a novel type. If the H20 molecules are not considered, the ion packing in both hydrates may be regarded as of the anti-NiAs type. The ion packing in R4EX structures and the conformation of the Et4N+ ion in crystals are discussed in some detail. In this series of investigations we are interested in discovering how the idealized symmetry (Td or subgroup) of tetraradial" XL: ' species is reflected in the crystallographic symmetry when XL2' is incorporated in a crystal, on its own (n = 0) or in combination with another, not necessarily tetraradial species, and in particular how the packing type is affected by the size and complexity of XLI;' in simple chemical combinations. In the present contribution to the systematic crystal chemistry of such species we report the results of a redetermination of the structure of Et4NI and of determinations of the structures of Ph4PBr.H20 and Ph4PBr.2H20. Although Ph4PBr rather than its hydrates was originally the compound to be investigated, we were unsuccessful in our attempts to obtain crystals of the anhydrous bromide (see ~xperimental) .5

Growth and Characterization of Tetraphenylphosphonium Bromide Crystal

“…The structure is as same as a previously reported dichloromethane-solvated TPPB crystal [16]. TPPB in water or ethanol forms the same dihydrate crystal TPPB (2H 2 O), which is an orthorgonal system and Pnma space group with a = 16.2842(10) Å, b = 10.8087(10) Å, c = 12.6638(12) Å and α = β = γ = 90 • , as previously reported [17]. The X-ray crystal structure data obtained in this work are summarized in the Supporting Information materials.…”

Comparison of binding of tetraphenylborate and tetraphenylphosphonium ions to cyclodextrins studied by capillary electrophoresis

“…For Ph 4 B ± , the hydrodynamic radius of 0.42 nm is significantly smaller than the distance B-H4 (from the central boron atom to the H atom at C4) of 0.54 nm determined from crystallography [27,28]. Similarly for Ph 4 P + , the hydrodynamic radius is 0.44 nm, and the P-H4 distance 0.55 nm [29,30]. Thus, the analytes do not behave simply as spheres with radii given by the distance between the central atom and the atom at the periphery of the phenyl ring.…”

“…With Ph 4 P + the crystallographic value of l = 0.55 nm [29,30] suggests r eff = 0.45 nm, and the effective radius of the ion containing freely rotating phenyl groups is calculated to be 0.49 nm. This is slightly larger than the internal radius of the g-CD cavity, 0.48 nm [35], and evidently marginally too great to allow the geometry of Fig.…”

Crystal chemistry of tetraradial species. Part 3. Salts of aliphatic Schiff bases crystallizable from aqueous media: crystal structures of five iminium tetraphenylborates and a 6-31G* ab initio study of simple iminium ions

“…Space group, C2/c. The H(N) and H(0) hydrogens were located from a difference map; the N-H and 0-H distanceso and the HOH angle were constrained in the refinements to 1.02 A, 1 . OO A, and 105", respectively.…”